1. Field of the Invention
The present invention relates to a protective enclosure for an ion gun, a device for depositing materials through vacuum evaporation comprising such a protective enclosure, and a method for depositing materials.
The present invention is more particularly intended to be used in the ophthalmic lens surface treatment, in particular for spectacles.
2. Description of Related Art
Whatever the mineral, organic or composite nature of their matrix, it is known that it is often necessary to apply a surface treatment to ophthalmic lenses once they have been manufactured, so as to reinforce some of their features or to provide them with particular characteristics.
Such treatment may be for example an antireflection coating and/or a hardening treatment.
The present invention relates even more particularly to that case when such treatment is effected by depositing a coating formed with at least one layer of material, and when such a deposition is performed through evaporation, and, very especially, through vacuum evaporation.
Most of the time, said coating is a multilayer coating, that is to say a coating involving stacking a plurality of layers on each other.
The various layers that are thus implemented may be made of different materials, of the same materials deposited according to various thicknesses, or even of the same materials coated according to similar thicknesses. In the latter case, the layers are deposited with different evaporation parameters so that their physicochemical properties be different.
For example, for an antireflection coating, the usual practice consists in forming a multilayer stack comprising low refractive index layers alternating with high refractive index layers and one hydrophobic layer.
Such an antireflection coating is formed in a device for depositing materials through vacuum evaporation, such as illustrated on FIG. 1 illustrating a known material deposition device.
The device for depositing materials through vacuum evaporation comprises a treating chamber 10 defined by side walls 11, a substrate holder 12, an ion gun 2 comprising an outlet 13 that is able to generate an ion beam 14 directed towards the substrate holder 12, a material source 15a (typically metal oxides and/or silica) that can evaporate through electron bombardment 15c, an electron gun 15b that is able to bombard with electrons said material source 15a to generate an evaporated material beam 17 directed towards the substrate holder 12, a gun cover 18 rotatably movable between a close position a) and an open position b) releasing the ion gun outlet 2, and a material source 16 that can evaporate by the Joule effect (typically hydrophobic materials),
Movable covers (not shown on FIG. 1) are positioned above the material sources 15a and 16.
The covers cover up the sources as long as the expected temperature for evaporating the material to be evaporated has not been reached. Once it has been reached, the covers are removed and the material deposition may start.
Most of the time, a great number of substrates are simultaneously treated. The substrate holder, which comes as a portion of a sphere, is pivotally mounted, and has a plurality of locations suitable to receive each a substrate to be treated. The locations are distributed around the rotation axis of the substrate holder.
Generally, the material source 15a is made of a support onto which the material to be evaporated is placed, for example a crucible or a plate. The evaporation of the material is most of the time due to an electron bombardment generated by the electron gun 15b. 
The treatment based on an ion gun aims either at preparing the surface of the substrate prior to depositing a layer (a so called IPC treatment for “Ion Pre Cleaning”), or, when depositing a layer, at making it denser (a so called IAD method for “Ion Aided Deposition”), at oxidizing it or making it transparent.
However, depositing materials from a material source and the treatment using an ion gun lead to soil problems both on the walls of the treating chamber and on the ion gun.
Indeed, the beam of materials that are evaporating from the evaporation source 15a comes as a broad cone, thus soiling both the walls of the treating chamber and the ion gun.
It is known that it is possible to control the angle or the width of the evaporating cone by modifying the evaporated material flow rate. It is possible to make the crucible size and/or the electron gun power vary, for example.
However, such control is hardly obtained in practice because changing these parameters, which are calibrated to obtain a desired deposition quality, may be detrimental to the deposition quality.
It is therefore almost impossible to direct the beam of evaporated materials or the evaporating cone solely towards the specimen carrier, in order to avoid a pollution of the side walls of the treating chamber and the ion gun.
Similarly, the evaporation of materials obtained from the material source resulting from the Joule effect 16 also causes a pollution of the walls of the vacuum chamber and of the ion gun.
A further problem is due, when using the ion gun, to the occurrence of soils which essentially form inside the ion gun.
The origins of such soils are highly varied. When the ion gun works normally, a parasite phenomenon of tungsten omnidirectional cathode sputtering (material forming the cathode) occurs, as well as a cathode sputtering of the material forming the diffuser (gas distributor, typically in stainless steel, titanium, carbon, tungsten, or tantalum . . . ) and/or of the anode of the ion gun.
An oxidation phenomenon also occurs when air is allowed to come in at the end of the layer deposition because the gun is extremely hot.
These soils do settle onto the ion gun. They are detrimental to the good functioning of the same and to deposition stable operating conditions.
The most heavily soiled parts of the ion gun are the lid, the upper and lower anode supports, the diffuser (titanium gas distributor), the anode and, to a lesser extent, the securing screws of these parts.
Prior to carrying out the ion beam emission onto the substrates, the ion gun is submitted to a priming step, during which a stainless steel cover is positioned above the ion gun. During this step, the ions emitted by the ion gun hit the lower surface of the cover and may cause a stainless steel sputtering.
The soils, generated by the ion gun, do settle onto fixtures, the false plate and the side walls of the treating chamber, and do accumulate with the soils generated by the evaporation sources. On the other hand, during the ion gun operation and when the cover is open, ions are emitted towards the substrates (IPC, IAD steps . . . ) but also towards the side walls of the treating chamber, which may cause, under some conditions:                the uncontrolled sputtering of the materials previously deposited onto these side walls. Such material uncontrolled sputtering leads to a pollution of the substrates, the interfaces and the stacks;        the ion reflection against the substrates, having a lower and uncontrollable energy.        
The soils generated by both the ion gun and the material evaporation sources onto the side walls of the treating chamber and the ion gun make it necessary to perform a demounting and a regular cleaning thereof.
Such cleaning comprises a sand blasting of the treating chamber walls and of the ion gun parts. Typically, such cleaning operation is performed approximately every 32 evaporation cycles to the maximum, or even more frequently for methods comprising IAD steps, and leads to the shutdown of the material depositing device.
In addition, once the ion gun and the walls of the treating chamber have been reassembled, it is necessary for the deposition device to be operational, to perform a degassing for at least 30 min so as to desorb the gases that are accumulated onto the large-sized side walls of the treating chamber.
These cleaning operations cause long-lasting and expensive maintenance times during which the deposition device is unserviceable.